This invention relates to apparatus useful in the rotary method of earth boring and more particularly to mud saver valves used between the kelly and drill pipe to prevent loss of mud when the connection between the drill pipe and kelly is broken.
The prior art includes U.S. Pat. Nos. 3,698,426 and 3,738,436 issued on the applications of Litchfield, et al and U.S. Pat. No. 3,698,411 issued on the application of W. R. Garrett, and the prior patents cited against the application that matured into these three patents. Further included in the prior art is a valve hereinafter sometimes called the Model A valve, which is a commercial embodiment of the valve shown in the aforementioned Garrett patent. The Model A valve is illustrated and described as prior art in the aforementioned Liljestrand application. An experimental valve, sometimes hereinafter called theh Model X valve, embodied the construction of the preferred embodiment illustrated in the Liljestrand application.
The disclosures of the above mentioned Litchfield et al and Garrett patents and the Liljestrand application are incorporated herein by reference.
Briefly, the Model A valve, as shown in FIGS. 1A and 1B of the accompanying drawing, includes a tubular body having integrally formed on its lower end a tapered threaded pin connector. At its upper end the valve has a tapered threaded box formed upon the upper end of a tubular top sub screwed into the body. The lower end of the top sub is beveled to provide a poppet valve type seat. A poppet valve closure engageable with the underside of the seat is provided with a tubular stem extending downwardly therefrom. A helical spring disposed in an annular chamber between the stem and body biases the closure to closed position. The stem is ported so that when drilling fluid pressure overcomes the spring and opens the valve, the fluid that has passed down through the valve can move radially inwardly into the stem. The stem carries a radial flange exposed on its upper face to fluid pressure when the valve is open, thereby holding the valve open without throttling. The flange forms the upper end of the annular chamber and is sealed to the body by a sliding plastics material O-ring seal, e.g. a seal with the trade name Polypak made of polyurethane filled with molybdenum disulfide. The lower end of the stem is also sealed to the body by a sliding plastics material O-ring seal. The pressure in the sealed chamber to which the lower side of the flange is exposed, is below the pressure of the drilling fluid, e.g. atmospheric. The aforementioned Garrett patent teaches that this chamber is to be provided with a vent port, and in the Model A valve such a port was provided but it was normally closed by a screw plug. The spring bears at its lower end against a body shoulder forming the bottom of the chamber and at its upper end against the flange. The stem is partable just above the flange, the upper and lower parts of the stem being threadedly connected. The lower portion of the stem is provided at its lower end with J-slots for engagement with a pulling tool to compress the spring. During assembly the spring is compressed with the pulling tool enough to allow the top sub threads to engage the body threads. Final compression of the spring is effected by makeup of the top sub in the valve body. A check valve in the poppet valve closure opens upwardly to communicate drill pipe pressure to the kelly when the drilling fluid pumps are shut down. The check valve closure includes a central portion or cap which is frangible for breakout with a sinker bar in case it is necessary to run a wire line tool through the valve. The cap is aluminum covered with rubber for better wear, the rubber having threads on its outer periphery to engage threads on a metal ring which, together with the cap, form the check valve closure.
The Model X valve, shown in FIG. 2A and 2B of the accompanying drawings, improved upon the Model A valve by providing the lower end of the top sub with a removable replaceable elastomer ring forming the poppet valve seat. The valve body is enlarged adjacent the ported portion of the poppet valve stem. The lower portion of the valve stem is divided into two parts connected by a straight threaded connection. There is a downwardly facing shoulder on the upper part and an upwardly facing shoulder on the lower part. A floating annular seal means includes a metal ring or bridge that overlies the lower stem shoulder and an upwardly facing shoulder at the lower end of the sealed chamber. The lower end of the spring bears on the bridge and the upper end of the spring bears on the upper shoulder of the stem. During assembly, with the floating seal ring bearing on the shoulder on the lower part of the stem the two parts of the lower portion of the stem are screwed together to precompress the spring enough to allow the top sub threads to engage the body thread. This eliminates the need for a pulling tool. When the sub is fully made up with the body the spring is further compressed, the floating seal ring bearing on the body shoulder as the lower stem shoulder moves down away from the ring. The ring has a tail portion of smaller outer diameter than the upper part of the ring, the tail portion sealing with the body below the body shoulder. This insures that the force of the upward fluid pressure on the ring, which is transmitted through the spring to the valve stem, is less than the downward force on the stem flange.
Sealing is improved by providing stationary smaller unidirectional polyurethane lip seals between the floating seal ring and body and larger sliding unidirectional lip seals between the ring and stem, and by providing unidirectional polyurethane lip seals between the body and stem flange mounted in a back-up ring captured between the upper and lower portions of the stem when they are screwed together. Orientation means on the seals prevent assembly in the wrong direction.
The Model X valve also included improvements over the Model A valve that are the contributions of the present applicant, as follows: the check valve closure of the Model X valve included threads on the break-out disc to engage the check valve closure ring, eliminating the rubber threads on the cover which sometimes slipped. The rubber cover was bonded to the break-out disc and had a skirt extending over the threaded juncture of disc and ring. The check valve closure was provided with a longer guide stem to prevent objectionable canting. Protuberant ribs or wings on the rubber cover of the check valve break-out disc, which wings were a result of the molding procedure, were eliminated, since they cause turbulence. In assembly, the skirt on the rubber wear cover was used as a hand grip in place of the wings on the Model A valve.